A variety of digital video processing technologies have evolved in recent years to meet the growing demand of the digital video display (e.g. digital television) market. One such technology that is continually being refined and improved is Digital Light Processing® technology, or DLP® technology, which provides all-digital projection displays that offer superior picture quality in terms of resolution, brightness, contrast, and color fidelity. Various DLP® solutions include progressive scan conversion, digital video resampling, picture enhancements, color processing, and gamma processing.
Gamma processing generally entails compensating for nonlinear signal-to-light characteristics. More particularly, the intensity of light generated by a physical device is not usually a linear function of the applied signal, thus requiring conditioning of the video signal to arrive at the desired output. Accordingly, technology has been developed to condition digital video signals to undergo a gamma correction process, which maps linear light intensity (the output image) to a non-linear voltage signal (the input video signal). The relationship between the input video signal and the light intensity output is often described in terms of a nonlinear transfer function.
Gamma correction can be implemented in a variety of ways depending on the image output desired by the manufacturer. For example, some implementations of gamma correction follow a standard gamma correction model, which is generally depicted as a parabolic curve 10 in FIG. 1. Standard gamma correction follows the 2.5 power law, which provides that the intensity produced at the face of the display is approximately the applied voltage, raised to the 2.5 power. However, it has been found that in some cases better contrast may be obtained through implementation of a gamma correction model having an “S-shaped” parabolic relationship 20 between the signal input and the light output, such as depicted in FIG. 2. While providing better contrast, these gamma correction models have poorer quality of excessively dark and excessively bright images. In essence, there is a tradeoff between better contrast for those images falling in the middle of the light intensity spectrum, and poorer contrast for those images lying on the fringes of this spectrum.
Gamma correction has heretofore been implemented at the front end of the video signal conditioning process. Manufacturers of digital televisions typically choose a particular gamma correction and implement this gamma correction during manufacture. Accordingly, the implemented gamma correction will remain the same regardless of the types of images displayed.